Food webs are diagrams depicting which species interact or in other words, who eats whom. An understanding of the structure and function of food webs is crucial for any study of how an ecosystem works, including attempts to predict which communities might be more vulnerable to disturbance and therefore in more immediate need of conservation. Although it was first published twenty years ago, Stuart Pimm's Food Webs remains the clearest introduction to the study of food webs. Reviewing various hypotheses in the light of theoretical and empirical evidence, Pimm shows that even the most complex food webs follow certain patterns and that those patterns are shaped by a limited number of biological processes, such as population dynamics and energy flow. Pimm provides a variety of mathematical tools for unravelling these patterns and processes, and demonstrates their application through concrete examples. For this edition, he has written a new foreword covering recent developments in the study of food webs and demonstrates their continuing importance to conservation biology.